In carburetors, the intake air breaks up the liquid fuel into droplets. Together the air and the atomized fuel form the combustible mixture for internal combustion engines. Unfortunately, there is only the small area around each droplet of liquid fuel that is vaporized, leaving the rest still in liquid form when this mixture enters the engine. It is the vaporous fuel combined with the air which gives an explosive mixture; and it is this mixture that can be exploded during the short engine power stroke time available. The remaining portion of fuel, still in liquid form, simply burns or exhausts to the environment; hence impairing the efficiency of the engine and polluting the environment. This situation is more apparent for low speed and low load operations when the intake air velocity is too low to effectively break up the fuel droplets. The fuel injection systems, employed for some internal combustion engines today, alleviate the problem to some extent by injecting the liquid fuel directly into the intake air stream via a nozzle to produce finer droplets and providing a more precise air/fuel mixture. Unfortunately, even the finer droplets remain mostly in liquid form.
Realizing this problem, there were numerous designs for vaporizing the fuel by inventors in the past and some of them were granted patents. However, the problems for making this concept practical have not been fully overcome. There have been many attempts to improve the vaporization state of the fuel by employing ultrasonic technology and engine exhaust heat for fuel vaporization. In this section, the shortcomings of these attempts and in particular the problems encountered with this type of carburetion, namely vaporization carburetion, will be outlined.
The most common designs to vaporize the fuel is to provide an exhaust gas heated, engine coolant heated, or electrically heated heat exchanger in between the conventional carburetor and the intake manifold. The main disadvantage of this type of designs is the overall heating of the intake air. This heating tends to promote detonation; the uncontrollable ignition of the fuel mixture inside the engine cylinder. Another disadvantage is the reduction of the maximum power output of the engine. As the intake air temperature increases, the air mass going into the engine decreases due to the physical property that at higher air temperatures, the air density is lowered. In effect the maximum power produced by the fuel and air explosion is lessened. Some of these designs divert a portion of the intake air and fuel into the heat exchanger. Subsequently, only a portion of the fuel is vaporized and the majority of the fuel is still in liquid form. In engine coolant heated systems, the temperature of the engine coolant is not high enough for fuel vaporization. In electrically heated systems, extra batteries may be needed for providing the electrical power to the heat exchanger, and in general extra engine power is needed to generate this electricity to be effective.
Other attempts involved employing ultrasonic technology to produce finer droplets. Commonly, an ultrasonic transducer, which is made of piezoelectric crystal, is mounted between the conventional carburetor and the intake manifold. As the intake air and the fuel pass through the ultrasonic transducer, some droplets of fuel come in contact with the ultrasonic transducer. Vibrating at high frequency, the transducer breaks the fuel into finer droplets. However, these finer droplets remain mostly still in liquid form. It is also known that air is a poor medium for ultrasonic wave transmission, therefore ultrasonic wave energy is substantially reduced to have little effect on the droplets which are not in immediate contact with this ultrasonic transducer.
Another approach is a stand alone carburetor which consists of a few basic modules for conditioning the fuel. This is the approach this invention is based on. Commonly, this design has four basic modules, they are a fuel atomization chamber, a heat exchanger, heat exchanger temperature control apparatus and fuel metering mechanism. Earlier attempts usually employ mechanical spray nozzle for fuel atomization with bulky heat exchanger, simple heat exchanger temperature control and fuel metering mechanisms.
One of the main problems encountered in vaporization carburetor is gumming. Gumming occurs when high molecular weight components of the fuel, referred to as high ends of the hydrocarbon, cannot vaporize and begin to stick to the heat exchanger surface, in effect lowering the efficiency of the heat exchanger to a stage that renders this approach impractical. Some designs have heater elements submersed in the fuel for fuel vaporization. Light ends of the hydrocarbon simply boil off and the high ends remain. Obviously, gumming is inevitable in this situation.
The disadvantage of employing mechanical spray for fuel atomization is the production of very coarse fuel droplets. As these droplets contact the heat exchanger hot surface, light ends of the hydrocarbon vaporize and cool the hot surface. Subsequently, high ends of the hydrocarbon cannot vaporize and start to accumulate.
Some designs introduce the amount of atomized fuel according to the engine demands; controlled by the engine vacuum or activated by the throttle position. Some designs simply rely on the intake air to meter the atomized fuel like the conventional carburetor does. These type of designs cannot satisfy transient requirements such as load variations, acceleration or deceleration because of the lag effects related to the fuel reaching the engine from its point of injection. This time delay is due to the time it takes for the fuel to pass through the heat exchanger.
Vaporization of fuel requires abundant heat. Commonly heat from the engine exhaust is used for this purpose because this heat is the waste byproduct from the consumed fuel. Most of the previous designs cannot make use of a large amount of engine exhaust because the engine exhaust is too hot to be injected in large quantity into the heat exchanger without risk of igniting the fuel inside. Realizing this difficulty, some designs divert only a portion of the engine exhaust into the heat exchanger. Unfortunately, the heat obtained from this portion of the exhaust is not adequate for thorough fuel vaporization. In addition to this, the exhaust gas flow is relatively slow which is considered to be laminar flow inside the heat exchanger. It is known that laminar flow yields poor heat transfer efficiency. In most cases, a large heat exchanger is required for thorough fuel vaporization.
Depending on the design, the divertion of the exhaust gas sometimes creates high engine exhaust back pressure. This high exhaust back pressure affects the efficiency of the engine. As the exhaust valve of the engine opens, it is desirable to expell the exhaust gas out of the cylinder as freely as possible. However, if the passage of the exhaust is obstructed to divert the exhaust gas into the heat exchanger, the extra engine power would be needed to push the exhaust gas out of the engine cylinder.
Another problem associated with making the vaporization carburetor practical is the control of the heat exchanger temperature. The temperature of the engine exhaust varies with different operating conditions of the engine. In particular, the temperature control is fairly demanding during transient situations such as; load variations, acceleration and deceleration. The temperature of the engine exhaust is high enough to ignite the fuel, therefore as more engine exhaust is diverted into the heat exchanger, more demands are placed upon the temperature control mechanism. In addition, as the fuel vaporizes, the heat exchanger requires more heat. Therefore means have to be provided to control the temperature of the heat exchanger in response to the incoming engine exhaust gas and the effect of the fuel vaporization in order to be effective.
The fuel prepared by the vaporization carburetor is highly explosive. This ensures a thermodynamic advantage when this explosive mixture is ignited inside the engine cylinder. Proper means have to be designed to protect this vaporous fuel from igniting in case of backfiring of the engine. Backfire occurs in an engine when the mixture is too lean, resulting in the time needed to complete the combustion being extended well into the intake cycle. A backfire arrester has to be able to arrest the fire and at the same time provide non-restrictive passage for the vaporous fuel.
The main advantage of the vaporization carburetor is the ability to extend the lean limit. The lean limit means the maximum air to fuel ratio for the engine without apparent backfiring, misfiring, detonation or any undesirable effect due to lean combustion. The effectiveness of fuel saving is the capability of the design to control the precise air to fuel ratio in all operations of the engine. The previous inventions apparently have not addressed this fundamental problem. Although a vaporization carburetor offers advantages in fuel economy and exhaust emission, making this concept practical is not an easy process.